In recent years the widespread use of antibacterial agents, in the form of chemically-based antibiotics, such as penicillin or tetracycline, has led to a huge increase in antibiotic-resistant bacterial strains. Mutations conferring antibiotic resistance, or genes encoding antibiotic resistance enzymes, such as penicillinases, are becoming increasingly common in pathogenic bacteria world-wide. Methicillin-resistant Staphylococcus aureus (MRSA) bacteria, for example, are an increasingly common form of infection, often acquired during surgery for other causes at hospitals. MRSA infections are extremely difficult to treat using conventional antibiotics.
One alternative approach to treating bacterial infections with antibiotics is to infect the bacteria with a virus, known as a bacteriophage. Such “bacteriophage therapy” was first developed early in the twentieth century, but was rarely used in the West after the advent of antibiotics in the 1940s.
Bacteriophages are specific to certain bacterial cell types. They cannot infect the cells of more complex organisms because of the differences in key intracellular machinery and cell-surface components. Most bacteriophages have structures, such as tail fibers, which enable them to bind to specific molecules on the surface of their target bacteria. Viral DNA, usually encased within the bacteriophage head, or RNA in some bacteriophages, is then injected, usually through the tail, into the host cell. In the case of obligate lytic phages, the injected viral DNA/RNA goes on to direct the production of bacteriophage progeny using the intracellular mechanisms of the host cell. The host cell is killed by lysis at the end of the cell cycle.
Staphylococcus bacteriophage K is a member of the diverse Myoviridae bacteriophage family. A paper by O'Flaherty S. et al. (J. Bacteriol. (2004), 186(9) 2862-2871) describes the sequence of the DNA genome of Staphylococcal phage K which carries 118 putative open reading frames (ORFs). Phage K has been previously characterized as an anti-MRSA phage. O'Flaherty S. et al. (Appl. Environ. Microbiol. (2005), 71(4) 1836-1842) studied phage K on different drug-resistant strains of S. aureus. 
WO 2009/044163 describes an anti-bacterial composition comprising phage K and/or phage P68 in a sufficiently high concentration to induce lysis-from-without in bacteria.
Methicillin-resistant Staphylococcus aureus (MRSA) can cause systemic infections or abscesses and ulcers, especially in sick, elderly or immune-compromised patients. It is increasingly a major cause of, or contribution to, death in hospitals. MRSA may reside in the nasal cavity of doctors or visitors without any apparent disease symptoms. However, the bacteria may be spread from person to person, including to patients. Accordingly, killing the bacteria assists in the prevention of the disease.
Hospitals currently utilise alcoholic hand-washes to help prevent MRSA being transmitted. However, such alcoholic washes are often not suitable for use on the sensitive lining of the nasal cavity or broken areas of skin. Therefore, there is a need to produce a composition suitable for killing bacteria, such as Staphylococcus aureus and in particular MRSA.
An object of the invention is to provide an alternative bacteriophage which provides effective antibacterial activity against Staphylococcus strains and in particular MRSA.